Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 290016
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
516 PM PDT THU APR 28 2016

UPDATED MARINE AND AVIATION SECTIONS

.DISCUSSION...28/12Z NAM/GFS/EC IN.

ITS A BIT DIFFICULT TO DETERMINE THE HEMISPHERIC WAVE NUMBER THIS
AFTERNOON AS THERE ARE MULTIPLE CUTOFF LOWS AROUND THE
GLOBE...BUT IT LOOKS TO BE 4 OR 5. EITHER WAY...THE PATTERN LOOKS
PROGRESSIVE...AT LEAST INITIALLY. THERE WILL LIKELY BE SOME
BLOCKING DEVELOPING IN THE EXTENDED PERIOD.

CURRENTLY THERE IS NORTHERLY FLOW ALOFT OVER THE AREA BETWEEN A
CUTOFF LOW OVER SOUTHERN NEVADA AND A WEAK RIDGE OFFSHORE. THIS
AFTERNOON LOOKS TO BE MOSTLY DRY AND A BIT WARMER THAN WEDNESDAY.
SOME LIGHT SHOWERS PERSIST AT THIS TIME OVER THE UMPQUA
BASIN...BUT THOSE WILL END SOON.

THE RIDGE WILL WEAKEN FRIDAY AND A STRONG SHORT WAVE WILL DIVE
DOWN THROUGH OREGON FRIDAY AFTERNOON AND EVENING. THE CURRENTLY
FORECAST TRAJECTORY IS A BIT FARTHER WEST THAN INDICATED BY THE
MODELS YESTERDAY. THIS SUPPORTS A BIT MORE CONVECTION FARTHER WEST
OVER THE MEDFORD CWA. HOWEVER...MODEL LIFTED INDICES ARE STILL NOT
BULLISH ON CONVECTION...ALTHOUGH THEY ARE TRENDING HIGHER AND
FARTHER WEST WITH SOME INSTABILITY.

IN THE WAKE OF THE WAVE...A LONG WAVE RIDGE WILL BUILD IN FROM
THE WEST SATURDAY. FLOW ALOFT WILL TURN NORTH FRIDAY NIGHT INTO
SATURDAY AND THEN NORTHEASTERLY SATURDAY NIGHT. THIS WILL SET UP
AN OFFSHORE LOW LEVEL FLOW EVENT WHICH WILL PEAK SATURDAY NIGHT.
EXPECT CLEAR SKIES AND WARMER TEMPERATURES...ESPECIALLY ON THE
RIDGES. IT WILL ALSO BE BREEZY ON THE RIDGES. FLOW WILL REMAIN
OFFSHORE SUNDAY NIGHT...BUT WINDS WILL BE WEAKER. RH RECOVERIES ON
THE RIDGES WILL LIKELY BE MODERATE THAT NIGHT.

ALL OF THE MODELS BACK A SHORT WAVE OVER THE AREA FROM THE EAST
SUNDAY AFTERNOON AND EVENING. A WAVE WITH SUCH A TRAJECTORY AFTER
AN OFFSHORE EVENT WILL MOST LIKELY NOT HAVE MUCH MOISTURE TO WORK
WITH...AND THE TIME SECTIONS INDICATE IT WILL REMAIN VERY DRY
BELOW AROUND 12000 FEET. LIFTED INDICES ARE ALSO MARGINAL...DROPPING
JUST BELOW ZERO OVER A FEW EAST SIDE LOCATIONS. THEREFORE...WILL
GO WITH GHOST POPS AND NOT MENTION ANY CHANCES OF SHOWERS AND
THUNDERSTORMS SUNDAY AFTERNOON AND EVENING.

HOWEVER...SUNDAY WILL BE THE WARMEST DAY WHEN THE THERMAL TROUGH
AXIS SLIDES NORTH OVER THE FORECAST AREA AND JUST AFTER OFFSHORE
FLOW REACHES A PEAK. HIGH TEMPERATURES WILL BE 10 TO 20 DEGREES
ABOVE NORMAL...EVEN ALONG THE COAST. THE LONG WAVE RIDGE WILL
AMPLIFY AS IT MOVES INTO THE INTERMOUNTAIN STATES SUNDAY
NIGHT...THEN IT WILL REMAIN THERE FOR A FEW DAYS. STOCKTON

EXTENDED DISCUSSION...MONDAY THROUGH THURSDAY. THE GFS CONTINUES
TO SHOW QPF BREAKING OUT MONDAY AFTERNOON. THE EC HAS BACKED OFF
ON THE AMOUNT OF QPF COVERAGE AND THE CANADIAN SHOWS NOTHING. IN A
NUTSHELL, MONDAY COULD BE A TOUGH CALL IN TERMS OF PRECIPITATION
AND THUNDERSTORMS THREAT. HOWEVER, AS MENTIONED IN YESTERDAY`S
EXTENDED DISCUSSION, THE UPPER LEVEL PATTERN IS NOT ONE THAT WOULD
BE FAVORABLE FOR CONVECTION, SO SUSPECT THE QPF FIELDS (ESPECIALLY
FROM THE GFS) MAY BE OVERDONE. NOTE: THE EC HAS BACKED OFF ON THE
AMOUNT AND COVERAGE OF THE QPF FIELDS FROM YESTERDAYS AND LAST
NIGHTS RUN. THE UPPER TROUGH ON MONDAY IS STILL WELL OFFSHORE AND
THE AMOUNT OF INSTABILITY IS MARGINAL AT BEST AND THERE IS LITTLE
OR NO TRIGGER. TUESDAY LOOKS MORE FAVORABLE FOR SHOWERS AND A
SLIGHT CHANCE OR ISOLATED THUNDERSTORMS. ESPECIALLY IN THE
AFTERNOON AND EVENING AS THE UPPER TROUGH MOVES CLOSER TO THE
COAST WITH SHORTWAVES BEING EJECTED AHEAD OF IT, THUS PROVIDING A
STRONGER TRIGGER. IN ADDITION INSTABILITY PARAMETERS ARE GREATER.
THE MODELS STILL SHOW THE LONG WAVE TROUGH NEAR OR OVER THE PAC NW
AND RIDGE IN THE ROCKIES NEXT WEDNESDAY THROUGH FRIDAY. WHILE THE
DETAILS DIFFER, THEY ALL SUGGEST IT COULD REMAIN UNSETTLED WITH
TEMPERATURES NEAR OR SLIGHTLY ABOVE NORMAL. -PETRUCELLI

&&

.AVIATION...FOR THE 29/00Z TAF CYCLE...VFR WILL PREVAIL INLAND
SOUTH OF THE UMPQUA DIVIDE AND FROM THE CASCADES EASTWARD TONIGHT
THROUGH FRIDAY AFTERNOON. AREAS OF MVFR CIGS ALONG THE COAST NORTH
OF CAPE BLANCO WILL OVERSPREAD MOST OF THE UMPQUA VALLEY OVERNIGHT
INTO FRIDAY MORNING. A COLD FRONT WILL MOVE ACROSS THE AREA FRIDAY
WITH ISOLATED TO SCATTERED SHOWERS. ISOLATED THUNDERSTORMS MAY FORM
OVER THE EAST SIDE IN THE AFTERNOON. GUSTY NORTHWEST WINDS WILL ALSO
DEVELOP FRIDAY AFTERNOON, ESPECIALLY OVER THE EAST SIDE. SPILDE

&&

.MARINE...UPDATED 230 PM PDT THU 28 APR 2016...NORTHWEST WINDS
AND STEEP SEAS WILL EASE FROM NORTH TO SOUTH THIS EVENING
AND OVERNIGHT AS OFFSHORE HIGH PRESSURE WEAKENS. A COLD FRONT WILL
MOVE THROUGH THE WATERS LATE FRIDAY MORNING WITH ANOTHER ROUND OF
GUSTY NORTH WINDS FRIDAY AFTERNOON AND EVENING. OFFSHORE HIGH
PRESSURE WILL REBUILD RAPIDLY FRIDAY NIGHT WITH A THERMAL TROUGH
SETTING UP ALONG THE COAST SATURDAY. THIS WILL RESULT IN THE
POTENTIAL FOR GALE FORCE WINDS AND HIGH, VERY STEEP SEAS SOUTH OF
CAPE BLANCO. WINDS AND SEAS GRADUALLY EASE SUNDAY INTO MONDAY. SPILDE

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.

CA...NONE.

PACIFIC COASTAL WATERS...GALE WATCH FROM SATURDAY MORNING THROUGH
     LATE SATURDAY NIGHT FOR PZZ356-376.
     SMALL CRAFT ADVISORY UNTIL 5 AM PDT FRIDAY FOR PZZ356-376.

$$

MAS/JRS/MAP


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